To better understand the mechanisms underlying trigeminal neuromuscular function the mandibular motor system will be evaluated by looking at its fatigue - endurance and tremor characteristics under a variety of experimental conditions. These two areas of investigation will help characterize two interrelated aspects of trigeminal motor physiology. Two series of muscle fatigue-endurance experiments will be performed using protrusive, retrusive and closing jaw muscle force measurements: 1) with surface EMG monitoring of whole muscle activity and 2) with fine wire electrodes placed in individual jaw muscles to evaluate the contractile properties of individual single motor units. The fatigue endurance studies will evaluate maximum voluntary force and peak EMG levels, EMG frequency spectrum, and EMG isometric activation levels. This analysis will be done at various isometric force levels monitoring the jaw closing, protrusive, and retrusive muslces. Using different percentages of the maximum force (protrusive, retrusive, and closing) will allow analysis for any differential effect that theoretically activating small vs. large motor units may have. Two tremor studies will be performed: 1) using accelerometers to evaluate jaw tremor at rest and 2) using force oscillatioins and computer averaging techniques to evaluate tremor at different levels of isometric force. The tremor studies will evaluate tremor frequency and the correlation of motor unit synchronization versus cardioballistic vibration as contributing factors. In general these various studies will be performed on over 140 normal jaw function subjects but this research proposal will include at least 60 subjects with myofascial pain in the later stages. Gathering the information proposed in this research protocol is essential for the development of a better understanding of trigeminal neuromuscular function in normal subjects and will give insight into the disease process underlying abnormal function of the masticatory motor system.